The Center's Central Hypothesis posits that layer 3 pyramidal cells (PCs) in subjects with schizophrenia have a cell type-autonomous pathology that is refiected in altered somatodendritic morphology and that differs in severity across regions in the cortical visual working memory and attention network. These abnormalities of layer 3 PCs result in locally reduced excitatory drive, refiected in reduced markers of metabolic activity in layer 3 PCs and reduced activity-dependent markers in reciprocally-connected layer 3 parvalbumin (PV)-expressing basket cells. This model leads to several novel predicfions. For example, that deflcits in layer 3 PC somal volume and dendritic spine density are present in mulfiple cortical regions, but moderated by region-specific factors (Aim 1). To date only limited analyses of primary visual cortex (VI) have been conducted, and the posterior parietal cortex (PPC) has not been examined. Our preliminary data indicate that impairments in dorsolateral prefrontal cortex (DLPFC) are associated with reduced markers of local network activity within PCs and PV basket cells. Functional data indicate impaired activity within VI and PPC during visual tasks in subjects with schizophrenia. Thus, our model predicts that markers of neuronal acfivity are also altered within VI and PPC (Aim 2). Finally, reducfions in pre-synapfic proteins such as synaptophysin and synapsini, that are known to impair glutamatergic bouton funcfion, behavior, and cognifion, have been previously observed in schizophrenia. Our model predicts that reductions in these proteins predominate in intracortical glutamatergic boutons within layer 3 across V1-PPC-DLPFC and are posifively correlated with the magnitude of the underlying somatodendrific abnormalifies within regions in the network (Aim 3). This project serves as an essenfial link between disease-related molecular findings in these same neurons, layers and regions (Project 1) and abnormal information processing in disease (Project 5). This project will constrain the interpretation of how normative functional connectivity (Projects 4 & 5) is altered in disease (Project 5) and will guide predicfions for future studies using markers specific for projections between PPC and DLPFC that may be identified in Project 3.